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FORESTE 

COU.C6E  Of  AA6IUCW.T 


BULLETIN    OF 

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No.  72 


Contribution  from  the  Forest  Service,  Henry  S.  Graves,  Forester. 
May  29,  1914. 


SUITABILITY  OF  LONGLEAF  PINE  FOR  PAPER  PULP. 

By  HENRY  E.  SURFACE,  Chemical  Engineer  in  Forest  Products,  and  ROBERT  E.  COOPER, 

Chemist  in  Forest  Products. 

SOUTHERN  PINES  FOR  KRAFT  PULP. 

The  southern  pines  have  not,  until  within  the  last  few  years,  been 
considered  suitable  for  paper  pulp.  Their  resinous  nature  is  the 
chief  drawback  in  most  processes  of  paper  making.  The  recent 
development  in  Europe,  especially  in  Sweden  and  Norway,  of  the 
sulphate  process,  however,  and  the  superior  quality  of  the  product 
made  from  resinous  woods  has  turned  attention  to  longleaf  and 
other  southern  pines  as  a  possible  source  of  pulp  in  this  country. 
These  pines  have  long,  thick-walled  fibers,  and  also  high  specific 
gravities,  implying  large  yields  per  cord,  and  therefore  seem  particu- 
larly adapted  for  the  manufacture,  at  low  cost,  of  strong  wrapping 
papers.  The  waste  wood  from  the  lumber  industry  in  the  South  sug- 
gests a  source  of  cheap  raw  material. 

While  the  sulphate  process  can  be  used  in  the  manufacture  of 
bleaching  pulps,  its  principal  product  is  an  undercooked,  nonbleach- 
ing,  brown  pulp  known  as  "kraft"  pulp,  the  term,  a  German  one, 
signifying  strength.  True  to  its  name,  this  pulp  produces  a  remark- 
ably strong  paper,  very  resistant  to  wear. 

Kraft  papers,  which  may  be  made  by  the  soda  as  well  as  by  the 
sulphate  process,  are  especially  adapted  for  wrapping  purposes. 
Wrapping  papers  stand  third  among  the  paper  products  of  the  United 
States,  being  exceeded  in  amount  and  value  only  by  news  and  book 
papers.  In  1909  the  production  of  wrapping  papers  of  all  kinds 
aggregated  764,000  short  tons,  with  a  value  of  $42,296,000.1  The 
value  of  wrapping  papers  imported  in  1912  was  $846, 500.2  Complete 

1  Tariff  Board  Report,  Pulp  and  News  Print  Paper  Industry,  1911,  p.  21.    Senate  Doc.  31,  62d  Cong., 
1st  sess. 

2  Bureau  of  Foreign  and  Domestic  Commerce,  Monthly  Summary  of  Commerce  and  Finance  for  Decem- 
ber, 1912,  p.  744. 

24542°— 14 1 


477615 


2  BULLETIN   72,   U.^S.    DEPARTMfcfrT*  OF   AGRICULTURE.    ' 

statistics  for  recent  importations  6*f  kraftTpap*e*r  are  not  available,  but 
in  1908,  three  years  after  its  introduction  into  the  United  States,  the 
imports  amounted  to  between  10,000  and  12,000  tons.1  In  1912 
the  imports  of  unbleached  sulphate  pulp  from  Sweden  alone  were 
approximately  21,600  short  tons,  and  from  Norway  8,400  short  tons.2 

Manila  wrapping  papers,  including  the  better  imitation  manilas, 
have  generally  been  considered  the  strongest  and  best  wearing,  but 
the  light-weight  kraft  papers  give  the  same  service  as  manilas  almost 
twice  as  heavy.  Although  strong,  light-weight  wrapping  papers  are 
made  in  this  country  from  sulphite  pulps,  the  imported  kraft  papers 
and  papers  made  from  imported  kraft  pulps  have  proved  too  formidable 
competitors  for  even  the  best  wholly-domestic  product  of  this  kind. 
The  immediate  success  and  largely  increasing  use  of  kraft  products 
has  brought  on  the  market  imitations,  colored  to  resemble  the  gen- 
uine, made  from  strong  sulphite  pulp  or  from  such  pulp  together  with 
ground,  steamed-wood  pulp.  Although  some  of  them  are  quite 
strong  in  the  light  weights,  they  are  not  equal  to  the  genuine  in  other 
ways.  The  opportunity  for  developing  an  increased  domestic  output 
of  kraft  products  from  native  woods  is  apparent. 

The  above-mentioned  conditions  led  the  Forest  Service  to  conduct 
a  series  of  tests  at  the  Forest  Products  Laboratory,  maintained  in 
cooperation  with  the  University  of  Wisconsin,  Madison,  Wis.,  in  order 

(1 )  to  determine  the  suitability  of  the  southern  pines  for  paper  pulps ; 

(2)  to  ascertain  the  effects  of  varying  cooking  conditions  in  the  sul- 
phate process  of  pulp  making;  (3)  to  compare  the  sulphate  process 
with  the  soda  process.     Only  longleaf  pine  has  so  far  been  used  in  the 
tests,  of  which  this  bulletin  gives  the  results  under  such  preliminary 
analyses  as  have  been  made  at  this  time. 

LUMBER  WASTE  AVAILABLE  FOR  PULP  MAKING. 

The  total  stand  of  longleaf  pine  (privately  owned)  was  estimated 
by  the  Bureau  of  Corporations  in  1910  at  232  billion  feet  board 
measure,  while  for  all  southern  pines  the  amount  was  placed  at  384 
billion  feet.  The  lumber  cut  from  these  pines  in  1910  amounted  to 
14  billion  feet.  The  sawed  lumber  represents  approximately  one- 
half  the  volume  of  the  log  as  it  comes  to  the  mill.  Bark  and  saw- 
dust, which  are  valueless  for  paper  making,  constitute  a  large  pro- 
portion of  the  waste,  but  it  is  safe  to  say  that  20  per  cent  of  the 
volume  of  the  log,  exclusive  of  the  bark,  is  lost  in  slabs,  edgings,  and 
trimmings.  Tops  and  defective  logs  left  in  the  woods  and  small  logs 
which  at  present  are  converted  into  lumber  with  little  or  no  profit 
would  furnish  a  supply  of  raw  material  for  pulp  making  even  greater 
than  that  derived  from  the  mill  waste. 

1  Pulp  and  Paper  Investigation  Hearings,  1909,  Vol.  V,  p.  3041.    House  Doc.  1502,  60th  Cong.,  2d  sess. 

2  From  estimates  made  by  the  Swedish  Wood  Pulp  Association  in  1913  and  furnished  the  Forest  Service 
by  Mr,  M,  Giatzler,  New  York  City. 


SUITABILITY   OF    LONGLEAF   PINE   FOR   PAPER  PULP.  3 

The  waste  wood  mentioned  is  not  as  a  rule  the  clean,  clear  material 
to  which  pulp  mills  have  been  accustomed.  But  when  the  soda  and 
sulphate  processes  are  employed,  the  presence  of  knots,  pitch  pockets 
and  streaks,  and  remnants  of  decayed  wood  and  bark  are  not  very 
objectionable.  The  expense  of  handling  and  preparing  slabs  and  other 
irregular  sizes  and  shapes,  however,  is  greater  than  for  round  pulp- 
wood,  so  the  initial  cost  of  such  material  must  be  low  enough  to  offset 
the  extra  cost  incident  to  its  use. 

PULP  MAKING  PROCESSES  APPLICABLE  TO  LONGLEAF  PINE. 

Four  or  five  mills  are  at  present  using  southern  pine  mill  waste 
for  the  manufacture  of  wrapping  paper  and  similar  products,  three  of 
which  employ  the  sulphate  process.  .  Several  other  sulphate  mills 
are  either  projected  or  in  course  of  construction.  Because  of  the 
resinous  nature  of  the  wood  the  preparation  of  paper  pulp  from  long- 
leaf  pine  is  confined  to  the  soda  and  sulphate  processes,  unless  special 
extraction  treatments  are  employed  preliminary  to  cooking. 

The  soda  process  consists  in  digesting  suitably  prepared  wood  with 
caustic  soda  (NaOH)  solution.  The  cooking  results  in  dissolving 
the  lignin  and  resin  constituents  of  the  wood,  and  separating  the 
individual  fibers  from  one  another.  The  action  depends  partly  upon 
the  direct  solvent  and  saponifying  power  of  the  caustic  soda,  and 
partly  upon  the  hydrolysis  of  the  wood  in  the  presence  of  water  at 
high  temperatures,  forming  organic  acid  products  which  unite  with 
the  alkali  present.  Cellulose,  of  which  the  fibers  are  chiefly  composed, 
withstands  the  cooking  action,  except  under  very  severe  treatment. 

The  spent  cooking  liquor,  or  "  black  liquor,"  is  separated  from  the 
pulp  fibers  and  evaporated;  the  residue  is  calcined  in  a  furnace,  and 
the  soda  compounds  are  recovered  as  "  black  ash/'  an  impure  sodium 
carbonate  (Na2CO3) .  This  ash  is  dissolved  in  water,  and  the  solution 
is  causticized  with  freshly  burned  lime;  the  resulting  caustic  soda  is 
again  used  in  cooking.  The  losses  of  soda  occurring  in  the  operations 
are  made  up  by  adding  fresh  soda  ash  (commercial  sodium  carbonate) 
previous  to  causticizing. 

The  sulphate  process  is  similar  to  the  soda  process,  except  that 
sodium  sulphide  (Na2S)  is  employed  as  a  cooking  chemical  in  addi- 
tion to  the  caustic  soda.  The  sodium  sulphide  is  derived  from  sodium 
sulphate  (Na2S04),  which  is  added  during  the  recovery  operations  to 
make  up  for  the  losses,  and  it  is  from  this  chemical  that  the  process 
derives  its  name.  The  sodium  sulphate  is  mixed  with  the  black  ash 
and  subjected  to  a  high  temperature  in  a  "smelter";  this  treatment 
reduces  it  to  sodium  sulphide,  although  the  reaction  is  not  complete. 
The  " smelt,"  containing  sodium  carbonate,  sodium  sulphide,  and 
unreduced  sodium  sulphate,  is  dissolved  in  water  and  the  solution  is 
causticized,  as  in  the  soda  process,  with  lime,  which  has,  however, 


4  BULLETIN   72,   U.    S.    DEPARTMENT   OF   AGRICULTURE. 

little  action  on  the  sulphide  and  the  sulphate.  During  cooking  the 
organic  acids  produced  react  with  the  sodium  sulphide1  as  well  as 
with  the  caustic  soda,  so  that  in  calcining  both  chemicals  are  recovered 
as  sodium  carbonate.  If  desired,  soda  ash  may  be  added  to  the  smelt 
solution  before  causticizing  in  order  to  increase  the  proportion  of 
caustic  soda  in  the  cooking  liquors.  Some  mills  have  also  found  it 
advantageous  to  mix  with  the  causticized  cooking  liquors  some  of 
the  black  liquors  diverted  from  the  recovery  operations. 

The  soda  and  sulphate  processes  can  be  applied  to  extracted  or 
steam-distilled  chips  from  which  rosin  and  turpentine  have  been 
removed.  Turpentine  can  also  be  obtained  from  resinous  chips 
during  the  cooking  operations  by  condensing  the  " relief"  from  the 
top  of  the  digester.  However,  the  turpentine  is  very  impure,  and 
in  the  case  of  the  sulphate  process  contains  organic  sulphur  compounds 
from  which  it  is  separated  with  great  difficulty. 

EXPERIMENTAL  METHODS. 

KINDS  OF  TESTS. 

The  tests  made  by  the  Forest  Service  were  of  two  classes :  (1 )  Auto- 
clave tests  and  (2)  semicommercial  tests.  The  autoclave  tests  com- 
prised several  series  of  cooks  made  to  determine  the  effects  of  varying 
the  cooking  conditions  of  the  sulphate  process.  The  semicommer- 
cial tests  include  cooks  made  by  the  soda  as  well  as  by  the  sulphate 
process.  The  semicommercial  sulphate  cooks  employed  such  cook- 
ing conditions  as  the  autoclave  tests  indicated  would  give  good 
results,  while  the  tests  using  the  soda  process  were  made  with  cooking 
conditions  that  would  give  results  comparable  to  those  obtained  from 
the  sulphate  cooks.  Because  the  semicommercial  tests  show  in  a 
more  direct  manner  the  possibilities  of  preparing  paper  pulp  from 
longleaf  pine,  they  will  be  discussed  before  the  autoclave  tests. 

WOOD  USED. 

The  test  material  consisted  of  longleaf  pine  (Pinus  palustris  Mill.) 
from  two  localities,  Perry  County,  Miss,  (shipment  L-3),  and  Tangi- 
pahoa  Parish,  La.  (shipment  L-176).  A  portion  of  the  former,  con- 
sisting of  edgings  containing  approximately  equal  amounts  of  sap- 
wood  and  heartwood,  was  used  for  cooks  176-1,  2,  and  3  of  the  semi- 
commercial  soda  tests  (Table  3),  and  another  similar  portion  of  the 
same  shipment  was  used  for  cooks  1  to  65,  inclusive,  of  the  autoclave 
tests.  The  average  bone-dry  weight  of  the  wood  used  in  these  auto- 
clave tests  was  30.4  pounds  per  cubic  foot  green  volume;  the  maxi- 
mum and  minimum  values  were  36.4  and  26.6  pounds,  respectively. 
The  wood  was  fairly  free  from  resin.  The  remaining  cooks  employed 

1  In  this  reaction  volatile  organic  sulphur  compounds  having  extremely  disagreeable  odors  are  produced. 
Unless  these  odors  are  eliminated,  or  held  in  check  by  proper  means,  sulphate  pulp  mills  are  highly  objec- 
tionable except  in  sparsely  populated  regions. 


SUITABILITY   OF    LONGLEAF   PINE   FOR   PAPER   PULP.  5 

two  butt  logs  (15  and  22  inches  diameter)  of  the  Louisiana  wood, 
including  all  of  the  sapwood  and  heartwood.  These  logs  were  quite 
resinous,  but  were  free  from  knots.  They  had  an  average  bone-dry 
weight  of  35.5  pounds  per  cubic  foot  green  volume.  The  maximum 
and  minimum  weights  were  40.1  and  32.3  pounds,  respectively,  for 
the  various  determinations. 

The  material  was  prepared  for  cooking  by  removing  the  bark 
and  sawing  the  pieces  across  the  grain  into  sections  five-eighths  inch 
thick,  which  were  then  split  into  chips  about  three-sixteenths  to 
one-fourth  inch  by  2  to  6  inches  across  the  grain.  The  chips  were 
screened  to  remove  sawdust,  and  each  lot  was  thoroughly  mixed  so 
as  to  be  uniform  throughout. 

APPARATUS. 

The  semicommercial  cooks  were  made  in  a  vertical,  stationary 
digester  *  consisting  of  a  cast-steel  cylindrical  shell  with  top  and  bot- 
tom cones,  with  a  capacity  of  about  62  gallons.  The  digester  was  fitted 
at  the  top  with  a  " relief"  or  vent  pipe,  a  pressure  gauge,  and  a 
thermometer;  and  at  the  side  with  a  gauge  glass  for  noting  the 
height  of  the  liquor.  The  bottom  was  arranged  for  " blowing"  the 
contents  after  cooking.  Heat  was  furnished  partly  by  passing  steam 
directly  into  the  digester  at  the  bottom  and  partly  by  two  steam 
coils  placed  inside  the  bottom  cone.  The  pressure  and  temperature 
were  regulated  by  admitting  either  more  or  less  steam  into  the  diges- 
ter and  by  relieving  any  excess  pressure  by  means  of  the  top  vent. 

The  autoclave  cooks  were  made  in  a  horizontal  rotary  autoclave 
with  a  capacity  of  about  2  gallons.  This  vessel  was  made  of  a  6-inch 
steel  pipe  with  blank  flange  ends,  fitted  with  trunnions,  to  one  of 
which  was  attached  a  pressure  gauge.  A  screw-joint  handhole 
opening  in  the  side  provided  for  charging.  Heat  was  furnished  by 
Bunsen-burner  flames  underneath  the  autoclave,  and  the  pressures 
were  regulated  by  increasing  or  decreasing  the  heat.  The  autoclave 
was  not  relieved  during  cooking,  and  no  observations  of  tempera- 
tures were  made.  The  cooked  pulps  were  not  blown,  as  in  the  case 
of  the  semicommercial  tests,  but  the  cooking  vessel  was  quickly 
cooled  and  the  contents  poured  out. 

PROCEDURE  IN  TESTING. 

The  liquor  charges  for  the  sulphate  cooks  were  prepared  by  mixing 
caustic  soda  and  sodium  sulphide  solutions  of  known  composition,  as 
determined  by  previous  analyses,  together  with  water  and  dry  sodium 
sulphate.  The  amounts  of  each  constituent  were  taken  in  such 
proportions  that  when  the  whole  mixture  was  charged,  with  the  chips, 

1  The  apparatus  used  in  the  semicommercial  cooks  is  practically  the  same  as,that  fully  illustrated  and 
described  in  U.  S.  Department  of  Agriculture  Bulletin  No.  80,  "Effects  of  Varying  Certain  Cooking  Con- 
ditions in  the  Productions  of  Soda  Pulp  from  Aspen,''  by  Henry  E.  Surface,  1914. 


6  BULLETIN   72,   U.   S.   DEPARTMENT  OF  AGRICULTURE. 

into  the  digester  or  autoclave,  the  amounts  of  each  chemical  per 
pound  of  chips  (bone-dry  basis)  was  in  the  desired  proportion,  and 
the  concentration  of  chemicals  in  the  digester  liquor  (including  the 
water  in  the  chips)  was  of  the  desired  degree.  For  soda  cooks  the 
procedure  was  similar,  except  that  caustic  soda  was  the  only  chemical 
to  be  taken  into  consideration.  The  general  procedure  in  conducting 
the  tests  was  as  follows: 

The  chips  to  be  used  for  a  cook  were  sampled  and  weighed.  By 
means  of  the  sample  the  amount  of  moisture  in  the  chips  and  the 
equivalent  bone-dry  weight  of  the  charge  were  determined.  The  chips, 
together  with  the  cooking  liquors,  were  then  charged  into  the  auto- 
clave or  digester,  and  the  vessel  closed.  After  a  cook  was  completed 
the  crude  pulp  obtained  was  washed  thoroughly,  pressed  to  remove 
water,  shredded,  weighed,  and  sampled  for  determining  its  equivalent 
bone-dry  weight.  The  pulp  was  then  mixed  with  water  and  treated 
in  a  Hollander-style  beating  engine1  with  the  roll  barely  touching 
the  bedplate  (light  brush)  until  the  soft  chips  in  the  pulp  had 
become  disintegrated  into  fibers  and  the  wet  fibers  had  a  smooth, 
slippery  feel.  The  beater  roll  was  then  pressed  hard  down  on  the 
bedplate  (stiff  brush),  and  the  beating  operation  continued  until 
the  pulp  was  suitable  for  making  wrapping  paper,  as  determined  by 
its  "feel."  The  beaten  pulp  was  then  screened  through  the  slots 
(0.012  inch  width)  of  a  diaphragm  pulp  screen.  In  all  cases  the 
screenings  obtained  were  so  small  in  amount  that  they  were  dis- 
regarded in  the  yield  calculations.  The  semicommercial  pulps  were 
run  over  a  Pusey  and  Jones  15-inch  Fourdrinier  paper  machine  into 
rolls  of  dry  paper,  while  the  autoclave  pulps  were  made  up  into  sheets 
on  a  small  hand  mold.  The  papers  thus  produced  contained  the 
experimental  pulps  alone,  without  the  addition  of  any  other  materials. 

DETERMINATION  OF  YIELDS  AND  PROPERTIES. 

The  yield  of  pulp  (bone-dry  basis)  is  usually  expressed  as  a  per- 
centage of  the  bone-dry  weight  of  the  chip  charge,  both  weights 
being  determined  as  explained  above.  When  yields  per  cord  are 
given  they  are  based  on  a  "solid  cord"  containing  100  cubic  feet  of 
clear  wood  (green  volume)  having  a  bone-dry  weight  of  35.5  pounds 
per  cubic  foot; 2  or  3,550  pounds  per  cord. 

The  strengths  of  the  papers  from  the  semicommercial  pulps  were 
determined  by  means  of  a  Mullen  paper  tester,  five  "pop  tests"  being 
made  on  double  thicknesses  of  each  paper.  The  value  is  expressed 
as  a  "strength  ratio,"  which  is  the  average  of  the  five  test  values  in 
pounds  per  square  inch  divided  by  the  average  sheet  thicknesses 

1  A  25-pound  Emerson  beater  was  used  for  the  semicommercial  tests  and  a  1-pound  Noble  and  Wood 
beater  for  tiie  autoclave  tests.    Both  makes  were  equipped  with  steel  fly  bars  and  steel  bedplate  bars. 

2  This  was  the  average  bone-dry  weight  of  the  two  butt  logs  of  long  leaf  pine  from  Louisiana,  the 
material  used  in  the  tests  for  which  yields  per  cord  are  given. 


SUITABILITY  OF   LOKGLEAF   PINE  FOR  PAPER  PULP.  7 

in  ten-thousandths  of  an  inch,  and  also  as  a  "strength  factor/'  which 
is  the  average  of  the  five  pop  tests  divided  by  the  weight  per  ream 
of  500  sheets  of  paper,  each  measuring  24  by  36  inches.  The  relative 
resistance  of  the  papers  to  wear  was  determined  by  crumpling  the 
sheets  in  the  hand,  and  all  other  properties  mentioned,  except 
strength,  were  determined  by  feel  or  by  observation  without  the  aid 
of  instruments. 

DEFINITIONS  OF  TERMS  USED. 

While  the  significance  of  most  of  the  terms  used  in  recording  the 
test  data  (Tables  1  to  10,  inclusive)  is  either  self-evident  or  sufficiently 
clear  in  view  of  the  previous  discussion,  there  are  several  which  may 
require  explanation. 

Water  in  chips. — The  amount  of  moisture  is  expressed  in  per- 
centage of  water,  based  on  the  calculated  bone-dry  weight  of  the 
chips. 

All  sodium  compounds  as  Na20. — This  is  the  sum  of  the  sodium 
oxide  (Na2O)  equivalents  of  the  amounts  of  the  several  constituents 
entering  into  the  chemical  charge.  "Total  Na2O"  has  an  analagous 
significance  in  the  soda  process. 

Sulphidity. — The  sulphidity  of  the  liquor  charge  is  the  percentage 
ratio  of  the  Na2O  equivalent  of  the  amount  of  sodium  sulphide 
(Na2S)  used  to  the  amount  of  all  sodium  compounds  present  expressed 
as  Na2O. 

Causticity. — This  has  a  similar  significance  with  respect  to  the 
amount  of  caustic  soda  (NaOH)  used. 

Initial  volume  of  digester  liquors. — The  digester  liquors  include  the 
water  in  the  liquor  charge,  together  with  the  water  in  the  chips  and 
the  water  condensed  from  the  steam  passed  into  the  digester  during 
cooking.  This  condensation,  of  course,  does  not  enter  into  the  calcu- 
lation of  the  initial  volume. 

Apparent  condensation. — The  apparent  condensation  is  the  differ- 
ence between  the  calculated  yiitial  volume  of  the  digester  liquors  and 
the  observed  volume,  as  read  from  a  water  gauge,  at  the  end  of  the 
cook.  It  roughly  represents  the  amount  of  steam  condensing  in  the 
digester  during  cooking,  but  does  not  take  into  account  the  volume 
of  the  pulp  and  the  differences  in  temperature  of  the  initial  and  final 
liquors,  nor  the  steam  and  liquid  lost  during  relief. 

SEMICOMMERCIAL  TESTS. 

SULPHATE  PROCESS. 

The  object  of  the  semicommercial  sulphate  cooks  was  to  secure  the 
best  quality  of  pulp  with  the  highest  possible  yield.  The  severity  of 
cooking  employed  depends  largely  upon  the  use  for  which  the  pulps 
are  intended.  If  bleaching  or  easy  bleaching  pulps,  such  as  are  used 
in  book  and  other  white  papers,  are  desired,  more  severe  cooking 


8 


BULLETIN   72,   U.    S.   DEPARTMENT   OP   AGRICULTURE. 


treatments  are  necessary  than  if  the  pulps  are  to  be  used  in  natural- 
color  wrapping  papers.  The  present  experiments  apply  more  espe- 
cially to  the  latter,  for  which  the  important  properties  are  strength, 
toughness,  and  resistance  to  wear.  The  terms  mild,  medium,  and 
severe  cooking,  and  undercooked,  well-cooked,  and  overcooked  pulps 
used  in  the  following  discussion  are  significant  only  with  respect  to 
the  object  of  the  tests. 

MILD   COOKING   TREATMENTS. 

The  less  severe  the  cooking  of  a  wood  the  larger  will  be  the  yield 
of  crude  pulp.  However,  there  is  a  point  at  which  the  pulp  will  begin 
to  lose  its  valuable  properties  for  making  wrapping  papers.  For  cook 
71  the  digesting  conditions  were  outlined  to  give  a  much  undercooked 
pulp  (see  Table  1),  but  the  treatment  given  the  wood  was  even  less 
severe  than  is  indicated  by  the  recorded  data,  since  a  portion  of  the 
digester  liquor  was  lost  through  leakage  soon  after  the  cook  had  been 
started.  The  crude  unbeaten  pulp  from  this  cook  was  full  of  soft 
chips,  which,  while  hard  enough  to  resist  the  action  of  a  stream  of 
water  under  pressure,  could  easily  be  picked  apart  with  the  fingers. 
The  paper  made  from  the  beaten  pulp  had  a  strength  factor  of  0.50, 
was  moderately  tough,  and  had  fair  wearing  properties.  As  a  wrap- 
ping paper  it  would  be  considered  of  medium  grade.  The  yield,  61.2 
per  cent,  or  2,172  pounds  per  solid  cord,  was  very  high,  considering 
the  quality  of  pulp  obtained.  Pulps  produced  under  less  severe 
cooking  conditions  had  higher  yields  (see  autoclave  tests,  pp.  14-24), 
but  the  quality  was  not  so  good,  as  evidenced  by  brittleness,  lack  of 
strength,  and  poor  wearing  properties. 

TABLE  1. — Record  of  semicommerdal  tests  using  the  sulphate  process. 


Liquor  charge. 

Initial 

volume 

of  di- 

Weight 

Initial  concentrations. 

gester 

Cook 

otchips 
charged 

Water 

I'M 

liquors 
per 

No. 

(bone- 
dry 
basis.) 

in 

chips. 

NaOH. 

NasCOs. 

Na2S. 

S02 
com- 
pounds 

Na2SO4. 

All 
sodium 
com- 

Caus- 
ticity. 

Sul- 
phid- 
ity. 

pound 
of 
chips 
(bone- 

as 

pounds 

dry 

Na2S03. 

as  Na2O. 

basis). 

Grams 

Grams 

Grams 

Grams 

Grams 

Grams 

171 

Pounds. 
38.62 

Perct. 
34.6 

per  liter. 
26.5 

per  liter. 
1.4 

per  liter. 
13.2 

per  liter. 

per  liter 
13.2 

per  liter. 
38.5 

Per  ct. 
53.3 

Per  ct. 
27.3 

Gallons. 
0.679 

77 

38.61 

34.7 

44.6 

2.7 

22.3 

2.9 

22.1 

64.9 

53.2 

27.3 

.538 

81 

23.97 

22.7 

60.4 

3.2 

30.0 

4.0 

30.0 

87.6 

53.4 

27.2 

.300 

85 

23.97 

22.7 

36.0 

1.9 

18.0 

2.4 

18.0 

52.3 

53.3 

27.3 

.500 

92 

23.97 

22.6 

48.0 

2.4 

30.0 

4.0 

30.0 

77.5 

48.0 

30.8 

.300 

98 

23.97 

22.6 

28.8 

1.4 

14.4 

1.9 

14.4 

41.8 

53.3 

27.4 

.500 

113 

25.38 

18.2 

34.2 

1.9 

17.1 

2.2 

18.5 

50.4 

52.6 

27.0 

.700 

138 

25.38 

18.2 

59.9 

3.0 

30.0 

3.9 

30.0 

87.0 

53.4 

.     27.4 

.400 

141 

25.38 

18.2 

60.0 

3.3 

15.0 

2.1 

30.0 

74.4 

62.4 

16.0 

.400 

146 

25.38 

18.2 

26.5 

1.4 

13.2 

1.8 

13.2 

38.5 

53.3 

27.3 

.680 

147 

26  67 

12.5 

26.5 

1.2 

13.2 

1.8 

13.2 

38.4 

53.4 

27.4 

.680 

148 

26.67 

12.5 

26.5 

1.2 

13.2 

1.8 

13.2 

38.4 

53.4 

27.4 

.680 

1  A  portion  of  the  digester  liquor  was  lost,  due  to  leaks  during  the  early  stages  of  cooking. 


SUITABILITY   OF    LONGLEAF    PINE   FOR   PAPER   PUtP.  9 

TABLE  1. — Record  of  semicommercial  tests  using  the  sulphate  process — Continued. 


Chemicals  charged  per  100  pounds  of  chips  (bone-dry 
basis). 

Duration  of  cooking. 

• 

Cook 
No. 

NaOH. 

— 

Na2S. 

S02 
com- 
pounds 
as 
NaaSOs. 

Na2S04. 

All 
sodium 
com- 
pounds 
as  Na20. 

Total. 

At 
zero 
gauge 
pres- 
sure. 

At 
maxi- 
mum 
gauge 
pres- 
sure. 

Maximum 
cooking 
temperature. 

Pounds. 

Pounds. 

Pounds. 

Pounds. 

Pounds. 

Pounds. 

Hours. 

Hours. 

Hours. 

°F 

°C 

171 

15.0 

0.8 

7.5 

.0 

7.5 

21.8 

3.0 

0.1 

2.8 

331 

166 

77 

20.0 

1.2 

10.0 

.3 

9.9 

29.1 

3.0 

.2 

2.3 

331 

166 

81 

15.1 

.8 

7.5 

.0 

7.5 

21.9 

3.0 

.1 

2.5 

331 

166 

85 

15.0 

.8 

7.5 

.0 

7.5 

21.8 

3.0 

.1 

2.5 

331 

166 

92 

12.0 

.6 

7.5 

.0 

7.5 

19.4 

3.0 

.25 

2.5 

331 

166 

98 

12.0 

.6 

6.0 

.8 

6.0 

17.4 

5.0 

.1 

4.3 

331 

166 

113 

20.0 

1.1 

10.0 

1.3 

10.8 

29.4 

3.0 

.25 

1.0 

331 

166 

138 

20.0 

1.0 

10.0 

1.3 

10.0 

29.0 

3.0 

.1 

2.8 

331 

166 

141 

20.0 

1.1 

5.0 

.7 

10.0 

24.8 

3.0 

.1 

2.5 

331 

166 

146 

15.0 

.8 

7.5 

1.0 

7.5 

21.8 

3.0 

.2 

2.3 

338 

170 

147 

15.0 

.7 

7.5 

1.0 

7.5 

21.8 

3.5 

.3    . 

2.8 

338 

170 

148 

15.0 

.7 

7.5 

1.0 

7.5 

21.8 

3.5 

.2 

3.0 

338 

170 

Digester  pres- 

Steam 

Appar- 

Duration of  beater 

sures  per  square 

ent  con- 

treatment. 

inch. 

pres- 
sure 

densa- 

Tj 

Cook 
No. 

per 
square 
inch 
at  di- 
gester 
inlet. 

tion 
per 
pound 
ofchips 
(bone- 
dry 
basis). 

Yield  of  crude 
pulp  (bone-dry 
basis). 

Total. 

At 
light 
brush. 

At 
stiff 
brush. 

Strength 
ratio 
ofpaper. 

Strength 
factor 
ofpaper. 

weight 
of 
papers 
tested. 

Maxi- 
mum 
gauge. 

Blow- 
ing. 

Lbs.  per 

solid 

Pounds. 

Pounds. 

Pounds. 

Gallons. 

Per 

cord. 

Hours. 

Hours. 

Hours. 

Pounds. 

171 

90 

40 

105 

10.20 

61.2- 

2,172 

3.5 

1.5 

2.0 

0.60 

0.50 

76 

77 

90 

40 

105 

.50 

•15.3 

1,609 

3.5 

2.0 

1.5 

1.15 

.91 

31 

81 

90 

50 

103 

.58 

47.9 

1,700 

5.0 

2.5 

2.5 

1.08 

.93 

44 

85 

90 

50 

108 

52.0 

1,846 

7.0 

3.0 

4.0 

.91 

.87 

38 

92 

90 

40 

110 

""."49" 

48.8 

1,733 

6.5 

2.5 

4.0 

.86 

.70 

28 

98 

90 

40 

108 

.50 

51.8 

1,839 

4.5 

1.0 

3.5 

.60 

.56 

28 

113 

90 

40 

100-95 

.32 

48.6 

1,725 

6.0 

2.0 

4.0 

.70 

.59 

37 

138 

90 

40 

110 

46.  1 

1,637 

141 

90 

40 

108 

44.2 

1,569 

8.5 

4.5 

4.0 

1.02 

.86 

36 

146 

100 

40 

105 

54.9 

1.949 

9.0 

4.0 

5.0 

.72 

.68 

45 

147 

100 

40 

115 

.41 

49.1 

1,743 

6.5 

4.0 

2.5 

.92 

.71 

37 

148 

100 

40 

115 

.63 

48.4 

1,718 

8.5 

4.0 

4.5 

•1.02 

.77 

33 

<P.  L.— 138,  S.  L.— 176.) 
1  A  portion  of  the  digester  liquor  was  lost,  due  to  leaks  during  the  early  stages  of  cooking. 

SEVERE  COOKING  TREATMENTS. 

The  effect  of  more  severe  cooking  treatments,  produced  mainly 
by  greater  initial  concentrations  and  amounts  of  active  cooking 
chemicals,  was  evidenced  by  the  thoroughly  cooked  or  overcooked 
pulps  from  cooks  77  and  141  (Table  1).  The  crude  pulps  were  not 
only  free  from  chips  and  shives,  but  also  seemed  to  be  soft  and 
fluffy.  The  papers  made  from  the  beaten  pulps,  however,  were  of 
very  superior  quality  with  regard  to  resistance  to  wear,  toughness, 
and  strength,  the  strength  factors  being  0.91  and  0.86  for  cooks  77 
and  141,  respectively.  Both  pulps  became  slightly  hydrated  during 
the  beater  treatments,  which  produced  a  parchmentizing  effect  and 
increased  the  strength  and  toughness.  Either  of  the  papers  could  be 
24542°— 14 2 


10 


BULLETIN   72,    U.    S.    DEPARTMENT    OF   AGEICULTUEE. 


rubbed  or  crumpled  for  a  long  time  without  becoming  fuzzy,  tearing, 
or  showing  signs  of  wear  at  the  place  of  friction.  The  papers  had  also 
a  soft,  smooth,  greasy,  leather-like  feel,  and  were  light  brown  in  color, 
like  the  imported  kraft  papers.  The  yields  were  rather  low  for 
sulphate  kraft  pulps.  For  cook  77  the  yield  was  45.3  per  cent,  or 
1,609  pounds  per  solid  cord,  and  for  cook  141,  44.2  per  cent,  or  1,569 
pounds  per  solid  cord.  Under  still  more  severe  cooking  treatments 
longleaf  pine  pulps  become  very  soft  and  gradually  lose  their  strength 
and  wearing  properties.  (See  autoclave  tests,  p.  14-24.) 

MEDIUM   COOKING  TREATMENTS. 

The  above-mentioned  cooks  show  approximately  the  higher  and 
lower  limits  of  yield  in  the  production  of  pulps  and  papers  of  good 
quality.  However,  the  better  quality  of  wrapping  papers  resulted 
from  pulps  having  the  lower  yields,  and  in  attempting  to  secure  this 
better  quality,  but  with  higher  yields  than  were  obtained  for  cooks  77 
and  141,  cooks  85,  98,  and  146  were  made.  For  cook  85  the  amounts 
of  chemicals  and  the  initial  concentrations  were  decreased  from  the 
corresponding  conditions  for  cook  77,  while  the  duration  of  cooking 
and  the  pressure  remained  practically  the  same;  for  cook  98  a  further 
decrease  was  made  in  the  amounts  of  chemicals  and  in  the  concen- 
trations, but  the  duration  of  cooking  was  increased;  for  cook  146  the 
amounts  of  chemicals  and  the  duration  were  practically  the  same  as 
for  cook  85,  but  the  concentrations  were  decreased  while  the  pressure 
was  increased.  The  cooking  conditions,  given  in  full  in  Table  1,  are 
briefly  summarized  in  Table  2.  The  resultant  papers  were  in  each 
case  of  good  quality,  being  tough  and  resistant  to  wear,  but  they  were 
in  general  not  so  strong  as  those  from  pulps  produced  under  more 
severe  cooking  treatments.  The  strength  factors  for  cooks  85,  98, 
and  146  were  0.87,  0.56,  and  0.68,  respectively.  There  is  little  doubt, 
however,  that  these  values  could  be  increased  considerably  by 
employing  beating  and  other  refining  treatments  better  adapted  for 
these  particular  pulps  than  the  treatments  given  them.  The  yields 
obtained  were  quite  high,  cook  85  yielding  52  per  cent,  or  1,846 
pounds  per  solid  cord;  cook  98,  51.8  per  cent,  or  1,839  pounds  per 
solid  cord;  and  cook  146,  54.9  per  cent,  or  1,949  pounds  per  solid  cord. 

TABLE  2. — Condensed  summary  of  cooking  conditions  for  cooks  77,  85,  98,  and  146. 


Cook  No. 

Liquor  charge,  initial 
concentrations. 

Chemicals  per  100 
pounds    of   chips 
(bone-dry  basis). 

Duration  of  cooking. 

Maximum 
gauge 
pressure 
per  square 
inch. 

Total. 

At  maxi- 
mum gauge 
pressure. 

NaOH. 

NaaS. 

NaOH. 

NasS. 

77... 

Grams  per 
liter. 
44.6 
36.0 
28.8 
26.5 

Grams  per 
liter. 
22.3 
18.0 
14.4 
13.2 

Pounds. 
20.0 
15.0 
12.0 
15.0 

Pounds. 
10.0 
7.5 
6.0 
7.5 

Hours. 
Z.O 
3.0 
5.0 
3.0 

Hours. 
2.3 
2.5 
4.3 
2.3 

Pounds. 
90 
90 
90 
100 

85.  . 

98  . 

146 

SUITABILITY   OF    LONGLEAF   PINE   FOE   PAPER  PULP.  11 

All  things  considered,  cooks  147  and  148,  which  may  also  be  classed 
with  those  of  medium  severity,  gave  the  best  results.  These  two 
cooks  were  made  under  almost  duplicate  cooking  conditions,  approxi- 
mately as  follows:  Caustic  soda  and  sodium  sulphide  charged  per  100 
pounds  of  chips,  15  and  7.5  pounds,  respectively;  initial  concen- 
tration of  caustic  soda  in  digester  liquor,  26.5  grams  per  liter;  initial 
volume  of  digester  liquor  per  pound  of  chips,  0.68  gallon;  total 
duration  of  cooking,  3.5  hours,  of  which  2.8  hours  for  cook  147  and 
3.0  hours  for  cook  148  were  at  a  maximum  gauge  pressure  of  100 
pounds  per  square  inch. 

The  crude  pulps  were  slightly  raw  and  contained  some  soft  chips, 
which,  however,  broke  up  in  the  beater.  The  pulp  from  cook  148 
was  hydrated  during  the  beating  treatment  to  such  an  extent  that  the 
paper  made  from  it  had  a  parchment-like  appearance,  the  individual 
fibers  being  scarcely  distinguishable  from  each  other.  This  paper 
had  good  wearing  properties  and  was  very  tough,  with  a  strength 
factor  of  0.77.  The  pulp  from  cook  147  was  not  subjected  to  so 
long  a  beating  treatment,  and  the  resulting  paper  was  not  parch- 
mentized  to  the  same  extent  as  that  from  cook  148.  It  had  a  strength 
factor  of  0.71,  however,  was  very  tough,  and  showed  good  wearing 
properties.  The  yield  from  cook  148  was  48.4  per  cent,  or  1,718 
pounds  per  solid  cord,  and  from  cook  147,  49.1  per  cent,  or  1,743 
pounds  per  solid  cord. 

EFFECTS  OF  BEATING. 

The  mechanical  treatment  given  a  kraft  pulp  has  as  important 
an  influence  on  the  properties  of  the  resulting  paper  as  the  cooking 
treatment  itself.  A  crude  pulp  which  appears  to  be  of  little  value 
can  be  made  into  strong  high-grade  paper  if  the  proper  beater  treat- 
ment is  employed,  while  the  best  pulps  can  easily  be  ruined  by 
improper  beating.  The  use  of  kollergangs  or  edge  runners  prelimi- 
nary to  actual  beating,  or  of  stone  rolls  and  bedplates  in  the  beaters, 
and  the  determination  by  successive  tests  of  the  refining  and  beating 
treatments  best  adapted  for  a  particular  pulp  undoubtedly  would 
have  resulted  in  papers  of  much  better  quality  than  those  obtained. 
Nevertheless,  many  of  the  experimental  papers  were  equal  or  superior 
to  commercial  kraft  papers. 

The  effect  of  different  beater  treatments  was  shown  by  a  single 
series  of  tests  on  some  of  the  crude  pulp  from  cook  71  (Table  1). 
Separate  portions  of  the  pulp  were  treated  in  the  1 -pound  beater 
for  periods  of  0.5,  1,  2,  3,  and  4  hours  with  the  roll  at  light  brush. 
The  papers  resulting  from  treatments  of  2  hours  or  less  were  soft  and 
weak,  and  had  poor  wearing  properties,  but  for  the  longer  periods  the 
papers  were  firm  and  tough,  with  good  wearing  properties.  Under 
the  4-hour  treatment  the  fibers  became  hydrated,  and  a  parchment- 
like  paper  resulted.  The  fibers  of  longleaf  pine  when  reduced  by  the 
sulphate  process  seem  to  take  up  water  and  to  become  hydrated  very 


12 


BULLETIN   72,   U.    S.   DEPARTMENT  OF   AGRICULTURE. 


quickly.  For  all  of  the  semicommercial  tests  previously  mentioned 
(Table  1)  this  effect,  indicated  by  the  smooth,  greasy  feel  of  the  wet 
paper  stock,  was  obtained  with  from  2  to  4  hours'  beater  treatment. 

WOOD  REQUIRED  FOR  1  TON  OF  PULP. 

It  has  been  shown  that  sulphate  kraft  pulps  of  fairly  good  strength 
and  toughness  can  be  obtained  from  longleaf  .pine  with  yields  (bone- 
dry  basis)  as  high  as  61  per  cent,  or  2,170  pounds  per  solid  cord  *  in 
case  of  wood  as  heavy  as  that  tested.  For  the  production  of  the 
best  grades  of  wrapping  papers,  which  equal  or  excel  in  quality  the 
imported  sulphate  kraft  papers,  the  yield  of  pulp  would  be  approxi- 
mately 51  per  cent,  or  1,800  pounds  (bone-dry)  per  solid  cord.  This 
is  equal  to  a  ton  (2,000  pounds)  of  nominally  air-dry  pulp.2  How- 
ever, it  should  be  remembered  that  for  wood  either  lighter  or  heavier 
than  that  on  which  this  calculation  is  based  the  amount  required  per 
ton  of  pulp  would  be  correspondingly  greater  or  less,  unless  the  differ- 
ences in  weight  were  due  to  resin  alone.3 

COMPARISON  OF  THE  SODA  AND  SULPHATE  PROCESSES. 

Table  3  contains  the  record  of  the  semicommercial  soda  tests. 
The  best  results  in  both  yield  and  quality  were  obtained  in  the  case  of 
cook  152.  This  cook  employed  20  pounds  of  caustic  soda  per  100 
pounds  of  wood  at  an  initial  concentration  of  79.7  grams  per  liter  and 
5  hours'  cooking  at  110  pounds  gauge  pressure,  the  total  duration 
being  6  hours.  The  resulting  paper  was  very  strong  (strength  factor 
0.90)  and  the  feel  and  wearing  properties  were  also  exceptionally 
good  for  a  soda  pulp.  The  yield  was  48  per  cent,  or  1,704  pounds 
per  solid  cord. 

TABLE  3. — Record  of  semicommercial  tests  using  the  soda  process. 


Cook 
No. 

Weight  of 
chips 
charged 

Water 
in 

Liquor  charge. 

Inital 
volume 
of  digester 
liquor  per 
pound  of 

Chemicals   charged    per    100 
pounds  of  chips  (bone-dry 
basis). 

Initial  concentrations. 

basis). 

NaOH. 

Na-jCOa. 

Total. 
Na20. 

Caustic- 

ity.    ' 

chips 
(bone-dry 
basis). 

NaOH. 

NaaCOs. 

Total. 
Na2O. 

Per 

Grams 

Grams 

Grams 

102. 

Pounds. 
23.97 

cent. 
22.6 

per  liter. 
84.0 

per  liter. 
3.4 

per  liter. 
67.1 

Per  cent. 
97.0 

Gallons. 
0.538 

Pounds. 
37.7 

Pounds. 
1.5 

Pounds. 
30.1 

136i 

25.37 

18.3 

59.9 

2.3 

47.8 

97.2 

.400 

20.0 

7.7 

16.0 

144. 

25.38 

18.2 

90.0 

3.4 

71.7 

97.2 

.400 

30.0 

1.1 

23.9 

149. 

25.89 

12.0 

90.2 

3.2 

71.8 

97.4 

.332 

25.0 

.9 

19.9 

150. 

25.  89 

12.0 

90.2 

3.2 

71.8 

97.4 

.332 

25.0 

.9 

19.9 

151. 

25.89 

12.0 

90.2 

3.2 

71.8 

97.4 

.332 

25.0 

.9 

19.9 

152. 

25.89 

12.0 

79.7 

1.8 

62.9 

98.3 

.301 

20.0 

.5 

15.8 

176-12 

41.89 

14.6 

90.0 

2.7 

71.3 

97.8 

.333 

25.0 

.8 

19.8 

176-2*. 

41.89 

14.6 

90.0 

2.42 

71.2 

98.0 

.266 

20.0 

.5 

15.8 

176-32. 

41.89 

14.6 

90.0 

2.42 

71.1 

98.0 

.267 

20.0 

.5 

15.8 

1  Weighing  3,550  pounds;  see  p.  6. 

2  Standard  moisture  content  of  10  per  cent  or  100  pounds  air-dry  weight  equals  90  pounds  bone-dry 
weight. 

3  The  average  specific  gravity  (oven-dry  weight,  green  volume)  of  all  of  the  longleaf  pine  from  Louisiana 
in  the  shipment  from  which  the  two  test  logs  were  taken,  including  bolts  cut  higher  up  in  the  trunks  of  the 
same  trees  and  material  from  several  additional  trees,  was  0.528.    (See  Forest  Service  Circular  213,  Mechan- 
ical Properties  of  Woods  Grown  in  the  United  States,  1913,  Table  1. )    This  is  equal  to  a  weight  per  cubic 
foot  of  33  pounds  in  comparison  with  the  35.5  pounds  obtained  for  the  two  butt  logs. 


SUITABILITY   OF    LONGLEAF   PINE   FOB  PAPER  PULP.  13 

TABLE  3. — Record  of  semicommercial  tents  using  the  soda  process — Continued. 


Cook  No. 

Duration  of  cooking. 

Maximum  cooking 
temperature. 

Digester  pressures 
per  square  inch. 

Steam 
pressure 
per 
square 
inch  at 
digester 
inlet. 

Apparent 
conden- 
sation per 
pound  of 
chips 
(bone-dry 
basis). 

Total. 

At  zero 
gauge 
pressure. 

At  maxi- 
mum 
gauge 
pressure. 

Maxi- 
mum 
gauge. 

Blowing. 

102... 

Hours. 
3.0 
6.0 
6.0 
6.0 
9.3 
4.5 
6.0 
7.0 
7.0 
8.0 

Hours. 
0.2 
.2 
.2 
.  2 
!3 
_  2 
'.'2 
.5 
.3 
.3 

Hours. 
2.5 
5.3 
5.5 
5.0 
8.3 
3.8 
5.0 
6.0 
6.0 
7.0 

°F. 
331 
331 
338 
338 
307 
361 
345 
338 
338 
338 

•c. 

166 
166 
170 
170 
153 
183 
174 
170 
170 
170 

Pounds. 
90 
90 
100 
100 
60 
140 
110 
100 
100 
100 

Pounds. 
40 
45 
40 
40 
40 
40 
40 

Pounds. 
115 
115 
110 
122 
120 
142 
125 
110 
115 
110 

Gallons. 
0.55 
.55 
.80 

136i  
144  

149     

150  

151  

1.02 
.55 
.94 
.76 
.91 

152 

176-12  
176-22  
176-32  

Cook 
No. 

Caustic- 
ity of 
black 
liquor  at 
end  of 
cook. 

Efficiency 
in  use  of 
NaOH. 

Yield  of  crude  pulp 
(bone-dry  basis). 

Duration  of  beater  treat- 
ment. 

Strength 
ratio  of 
paper. 

Strength 
factor  of 
paper. 

Ream 
weight  of 

B3S 

Total. 

At  light 
brush. 

At  stiff 
brush. 

102... 

Per  cent. 

Per  cent. 

Per  cent. 
47.2 
50.9 
39.8 
44.1 
52.0 
37.6 
48.0 
48.6 
51.1 
50.4 

Lbs.  per 
solid  cord. 
,676 
,808 
,413 
,566 
,846 
,335 
,704 

Hours. 
4.0 
6.5 
6.0 
6.5 
9.0 
6.0 
8.5 

Hours. 
2 
2 
6 
2 
5 
6 
4 

Hours. 
2.0 
4.5 
0.0 
4.5 
4.0 
0.0 
4.5 

0.43 
.55 
1.04 
1.04 
.53 
.91 
1.05 

0.41 
.54 
.84 
.84 
.56 
.80 
.90 

Pounds. 
42 
60 
48 
37 
43 
46 
37 

136  ! 

144... 

149.... 
150.  .  .  . 
151.... 
152.... 

176-1  2 

22.7 
41.6 
17.6 
11.2 

76.7 
57.3 
81.9 
88.6 

176-22. 
176-32 

1 

(P.  L.— 138,  S.  L.— 176;  P.  L.— 164-1.) 

1  Five  pounds  of  sodium  chloride  (table  salt)  per  100  pounds  of  chips  were  used  in  addition  to  the  chemicals 
indicated.    However,  it  will  be  shown  later  that  sodium  chloride  has  little  or  no  effect.    (See  p.  19.) 

2  Shipment  L-3a  from  Mississippi  was  used  as  the  test  material.    Data  for  these  three  cooks  have  been 
published  previously  in  Forest  Service  unnumbered  bulletin,  "Paper  Pulps  from  Various  Forest  Woods," 
by  Henry  E.  Surface,  1912.    Specimens  of  natural  color  and  bleached  pulps  accompanied  the  data. 

Cook  150  afforded  a  yield  of  52  per  cent,  or  1,846  pounds  per  solid 
cord,  but  the  quality  was  not  so  good  as  in  the  case  of  cook  152,  the 
paper  being  quite  weak  (strength  factor  0.56)  with  a  correspondingly 
low  resistance  to  wear.  The  papers  resulting  from  cooks  144,  149, 
and  151  were  all  of  very  good  quality,  having  high  strength  ratios 
and  good  wearing  properties,  but  the  yields  were  considerably  lower 
than  for  cook  152. 

Soda  pulps  from  longleaf  pine  tend  to  be  soft  and  fluffy,  even  when 
slightly  undercooked,  or  chippy.  Proper  beater  treatments  will 
remedy  this  to  some  extent,  but  the  pulp  does  not  become  so  well 
hydrated  nor  attain  the  same  smooth,  greasy  feel  during  beating  as 
the  sulphate  pulps,  and  the  resultant  papers  do  not  show  the 
parchmentized  effect  so  (characteristic  of  the  sulphate  papers.  On 
the  paper  machine  soda  stock  runs  "free,"  while  sulphate  stock  runs 
"slow,"  provided,  of  course,  both  kinds  of  stock  are  handled  simi- 
larly in  the  beater. 


14  BULLETIN   72,   U.    S.   DEPARTMENT   OF   AGRICULTURE. 

The  soda  papers  were  inferior  to  the  sulphate  papers  in  resistance 
to  wear;  the  latter  could  be  rubbed  and  crumpled  for  a  long  time 
without  showing  signs  of  wear,  while  the  former  had  a  tendency  to 
become  fuzzy  and  tear  under  similar  treatment.  Even  those  sul- 
phate pulps  at  very  high  yields  had  wearing  qualities  equal  to  the 
best  soda  pulps.  There  is  little  doubt  that  higher  yields  of  good 
kraft  pulp  can  be  obtained  with  the  sulphate  process  than  with  the 
soda  process.  Sulphate  pulps  of  fairly  good  quality  can  be  obtained 
with  yields  as  high  as  61  per  cent,  while  the  limit  for  soda  pulps  is 
approximately  50  per  cent.  With  higher  yields  the  soda  pulps  lose 
strength  and  toughness  and  become  brittle.  A  sulphate  pulp  with  a 
60  per  cent  yield  can  be  made  into  a  medium  grade  of  kraft  wrapping 
paper,  while  a  soda  pulp  having  the  same  yield  will  produce  only  a 
very  inferior  grade.  Considering  bursting  strength  alone,  equally 
strong  papers  can  be  made  by  either  process. 

The  main  advantage  of  the  sulphate  process  over  the  soda  process 
is  that  in  the  former  the  pulp  can  be  very  much  undercooked  and 
still  produce  a  fair  quality  of  paper,  while  a  soda  pulp  must  be  com- 
paratively well  cooked  before  a  good  paper  can  be  made  from  it. 
Moreover,  the  best  sulphate  kraft  pulps  were  obtained  with  a  total 
duration  of  cooking  of  only  3.5  hours,  while  in  the  soda  tests  6  hours 
were  required  to  secure  the  best  results. 

AUTOCLAVE  TESTS. 

The  autoclave  tests,  which,  as  previously  explained,  preceded  the 
semicommercial  tests,  were  made  to  determine  the  effects  of  varying 
the  cooking  conditions  in  the  production  of  sulphate  pulp.  The 
cooking  conditions  investigated  were: 

(1)  Amounts  of  the  various  cooking  chemical  employed. 

(2)  Cooking  pressures  or  temperatures. 

(3)  Durations  of  cooking. 

(4)  Initial  concentrations  of  chemicals  in  the  digester  liquors. 

Aside  from  the  chemicals  normally  present  in  sulphate  cooking 
liquors — that  is,  caustic  soda,  sodium  sulphide,  sodium  sulphate,  and 
sodium  carbonate,  the  effects  of  sodium  chloride  and  sulphur  in  con- 
junction with  caustic  soda  were  studied.  The  tests,  Tables  4  to 
10,  inclusive,  were  made  in  series,  in  any  of  which  all  cooking  con- 
ditions except  the  one  under  observation  were  held  as  nearly  constant 
as  possible. 

The  amounts  of  sodium  carbonate  and  of  SO2  compounds  expressed 
as  Na2S03  in  the  cooking  liquors  were  in  general  small  and  no 
mention  of  them  is  made  in  the  tabulated  data.  The  amounts  of 
sodium  sulphate  present  are  indicated  only  relatively,  except  in 
Tables  6  and  10. 


SUITABILITY   OF    LONGLBAF   PINE   FOR   PAPER  PULP. 


15 


EFFECTS  OF  VARYING  AMOUNTS  OF  CAUSTIC  SODA. 

The  effect  of  varying  amounts  of  caustic  soda  on  the  yield  of  crude 
pulp  is  shown  in  Table  4.  Two  series  of  tests  were  made,  differing 
in  the  amounts  of  sodium  sulphate  and  sodium  sulphide  employed. 
In  the  first  series  increasing  the  amounts  .of  caustic  soda  from  15  to 
90  pounds  per  100  pounds  of  wood  resulted  in  a  decrease  in  the  yield 
of  from  52  to  27.7  per  cent.  This  decrease,  however,  was  not  directly 
proportional  to  the  increase  of  caustic  soda  used,  as  values  of  this 
chemical  between  30  and  50  pounds  had  little  effect  in  varying  the 
yield.  For  higher  and  lower  values  the  effect  was  quite  pronounced. 
In  the  second  series  a  larger  amount  of  sodium  sulphide  was  used, 
and  consequently  the  yields  were  lower  for  corresponding  amounts  of 
caustic  soda,  but  variations  in  the  amounts  of  this  chemical  produced 
similar  effects. 

TABLE  4. — Effect  of  varying  amounts  of  caustic  soda  (NaOH)  on  the  yield  of  pulp. 

Weight  of  chips  charged  (bone-dry  basis) pounds. .    0. 986  to  1. 007 

Water  in  chips per  cent. .  10. 2      to  12. 6 

Initial  volume  of  digester  liquors  per  pound  of  chips  (bone-dry  basis) gallons..    0.650  to  0.690 

Duration  of  cooking,  total hours. . 

Duration  of  cooking  at  zero  gauge  pressure do 

Duration  of  cooking  at  maximum  gauge  pressure do 

Maximum  gauge  pressure  per  square  inch pounds. . 

Total  duration  of  beater  treatment  (at  light  brush  only) hours . . 


3.0 
0.1 
2.3 
90 
Oorl 


FIRST  SERIES. 


Liquor  charge. 

Chemicals   charged   per    100 

pounds  of  chips  (bone-dry 

Cook 

Initial  concentrations. 

basis). 

Yield  of 
crude 

No. 

pulp 
(bone- 

*A11 

Caus- 

Sulphid- 

All 

dry 

sodium 

ticity. 

ity. 

sodium 

basis). 

NaOH. 

Na2S.i 

com- 

NaOH. 

Na2S.i 

com- 

pounds. 

pounds, 

as  Na2O. 

asNa20. 

Grams 

Grams 

Grams 

per  liter. 

per  liter. 

per  liter. 

Per  cent. 

Per  cent. 

Pounds. 

Pounds. 

Pounds. 

Per  cent. 

31 

26.3 

13.1 

38.1 

53.6 

27.5 

15.0 

7.5 

21.7 

52.0 

55 

52.1 

13.0 

57.9 

69.7 

17.9 

30.0 

7.5 

33.4 

42.9 

56 

69.6 

13.0 

72.0 

74.9 

14.4 

40.0 

7.5 

41.4 

39.6 

57 

87.0 

13.0 

85.6 

78.7 

12.1 

50.0 

7.5 

49.2 

42.1 

58 

104.4 

13.0 

99.7 

81.1 

10.4 

60.0 

7.5 

57.3 

40.0 

59 

121.8 

13.0 

113.6 

83.1 

9.1 

70.0 

7.5 

65.3 

33.3 

60 

156.6 

13.0 

139.3 

87.1 

7.4 

90.0 

7.5 

80.1 

27.7 

SECOND  SERIES. 


29 

35.4 

44.4 

84.2 

32.6 

42.0 

19.9 

25.0 

47.4 

42.3 

28 

55.3 

45.9 

101.9 

42.1 

35.8 

30.0 

24.9 

55.2 

38.2 

33 

52.7 

43.9 

99.5 

41.0 

35.1 

30.0 

25.0 

56.6 

37.0 

54 

60.8 

43.3 

104.5 

45.1 

32.9 

35.0 

24.9 

60.1 

39.9 

32 

70.1 

43.9 

113.0 

48.5 

30.9 

39.9 

25.0 

64.4 

34.8 

27 

73.8 

45.9 

116.7 

49.0 

31.3 

40.0 

24.9 

63.3 

35.0 

53 

76.6 

43.3 

117.0 

50.8 

29.4 

44.1 

24.9 

67.3 

38.6 

43 

88.2 

44.3 

128.3 

53.2 

27.4 

49.8 

25.0 

72.5 

36.8 

26 

88.8 

44.4 

126.8 

54.3 

27.9 

50.0 

25.0 

71.4 

37.6 

49 

104.2 

43.4 

139.2 

58.0 

24.8 

60.0 

25.0 

80.2 

31.8 

52 

121.6 

43.2 

152.4 

61.9 

22.6 

70.0 

24.9 

87.8 

31.8 

51 

139.0 

43.5 

166.6 

64.6 

20.7 

80.0 

25.0 

95.8 

28.1 

(P.  L.— 138,  S.  L.— 3b.) 


1  With  a  few  minor  exceptions,  the  same  values  apply  to  the  Na2SO4. 

The  best  quality  of  pulp  was  obtained  with  cook  31,  using  15 
pounds  of  caustic  soda  per  100  pounds  of  wood.  This  resulted  in  a 
slightly  undercooked  product,  which  came  from  the  autoclave  in  the 


16 


BULLETIN   72,   U.    S.   DEPARTMENT   OF   AGRICULTURE. 


form  of  soft  chips.  The  chips  did  not  break  up  during  the  washing 
operation,  but  were  readily  pulped  by  beater  treatment.  The  pulp 
was  strong,  tough,  and  resistant  to  wear.  When  larger  amounts  of 
caustic  soda  were  employed  the  pulp  tended  to  be  soft,  fuzzy,  and 
less  strong,  while  for  smaller  amounts  it  was  harsh  and  brittle.  (See 
cooks  39  and  40,  Table  6.)  In  the  second  series  of  tests  (Table  4) 
the  conditions  were  such  that  all  of  the  pulps  were  overcooked  if 
considered  for  kraft  papers. 

The  higher  the  amount  of  caustic  soda  employed,  the  lighter  in 
color  was  the  pulp.  The  extremes  for  the  first  series  of  tests  were 
brown  in  the  case  of  cook  31  and  light  gray  in  the  case  of  cook  60. 
For  the  second  series  of  tests  the  color  change  was  less  noticeable. 

EFFECTS  OF  VARYING  AMOUNTS  OF  SODIUM  SULPHIDE. 

The  effects  of  varying  the  amount  of  sodium  sulphide  were  shown 
by  three  series  of  tests  employing  different  amounts  of  caustic  soda 
and  of  sodium  sulphate.  The  cooking  conditions  and  resultant  yields 
are  given  in  Table  5. 

TABLE  5. — Effect  of  varying  amounts  of  sodium  sulphide  (Na2S)  on  the  yield  of  pulp. 


0.! 


to    1. 043 


Weight  of  chips  charged  (bone-dry  basis) pounds. . 

Water  in  chips per  cent. .  11. 0      to  16. 0 

Initial  volume  of  digester  liquors  per  pound  of  chips  (bone-dry  basis) gallons. .    0. 662  to    0. 683 

Duration  of  cooking,  total hours. . 

Duration  of  cooking  at  zero  gauge  pressure do 

Duration  of  cooking  at  maximum  gauge  pressure do 2. 0     to 

Maximum  gauge  pressure  per  square  inch pounds. . 

Total  duration  of  beater  treatment  (at  light  brush  only) hours. 


3.0 
0.1 
2.5 
90 
0,  1,  or  2 


FIRST  SERIES.i 


Liquor  charge. 

Chemicals   charged  per    100 

Initial  concentrations. 

basis). 

Yield  of 

crude 

Cook 

pulp 

No. 

NaOH. 

Na2S.2 

All 
sodium 
com- 

Caus- 
ticity. 

Sulphid- 
ity. 

NaOH. 

Na2S.2 

All 
sodium 
com- 

(bone- 
dry 
basis). 

pounds, 

pounds, 

as  Na20. 

asNa2O. 

Grams 

Grams 

Grams 

31 

per  liter. 
26.3 

per  liter. 
13.1 

per  liter. 
38.1 

Per  cent. 
53.6 

Per  cent. 
27.5 

Pounds. 
15.0 

Pounds. 
7.5 

Pounds. 
21.7 

Per  cent. 
52.0 

34 

26.3 

26.3 

49.6 

41.1 

42.2 

15.0 

15.0 

28.3 

47.4 

35 

26.3 

43.9 

62.4 

32.7 

56.0 

15.0 

25.0 

35.5 

44.5 

36 

26.3 

70.2 

88.0 

23.2 

63.5 

15.0 

40.0 

50.0 

39.9 

37 

26.5 

88.3 

103.8 

19.7 

67.5 

15.0 

50.0 

58.9 

40.3 

SECOND  SERIES.' 


133 

27.2 

1.8 

31.1 

67.7 

4.6 

15.0 

1.0 

17.2 

68.9 

134 

27.2 

5.4 

34.4 

61.3 

12.6 

15.0 

3.0 

19.0 

67.6 

139 

27.0 

9.0 

37.3 

56.1 

19.2 

15.0 

5.0 

20.7 

60.1 

THIRD  SERIES. 


129 

35.3 

3.7 

39.4 

69.4 

7.4 

20.0 

2.1 

22.3 

64.3 

130 

35.9 

7.2 

43.0 

64.8 

13.3 

'20.0 

4.0 

23.9 

53.7 

131 

36.0 

10.8 

46.3 

60.2 

18.5 

20.0 

6.0 

25.7 

49.7 

132 

36.0 

14.4 

49.6 

56.2 

23.1 

20.0 

8.0 

27.6 

47.7 

(P.  L— 138.) 

1  The  Mississippi  wood  (shipment  L-36)  was  used  for  the  first  series  and  the  Louisiana  wood  (shipment 
L-176)  for  the  second  and  third  series. 

2  With  a  few  minor  exceptions,  the  Na2SO<  amounted  to  one-half  of  these  values  for  the  first  and  third 
series  and  to  two-thirds  of  these  values  for  the  second  series. 


SUITABILITY   OF    LONGLEAF   PINE   FOR  PAPER   PULP.  17 

In  the  first  series  of  tests,  with  an  increase  in  the  amount  of  sodium 
sulphide  from  7.5  to  50  pounds  per  100  pounds  of  wood,  the  yield 
decreased  from  52  to  40.3  per  cent.  For  amounts  of  25  pounds 
or  less  the  pulps  were  of  good  quality,  being  strong  with  good  wearing 
properties,  but  for  larger  amounts  the  pulps  became  soft  and  fuzzy 
and  evidently  were  overcooked. 

In  the  second  series,  increasing  the  amount  of  sodium  sulphide 
from  1  to  5  pounds  per  100  pounds  of  wood  resulted  in  a  decrease 
in  the  yields  from  68.9  to  60.1  per  cent.  The  largest  amount  (5 
pounds)  afforded  the  best  pulp,  considering  strength  and  wearing 
properties;  the  other  pulps  were  much  undercooked  and  quite 
brittle. 

The  third  series  of  tests,  using  a  larger  amount  of  caustic  soda 
(20  pounds),  showed  the  effect  of  increasing  the  amount  of  sodium 
sulphide  from  2.1  to  8  pounds  per  100  pounds  of  wood.  Under  these 
conditions,  the  yield  was  decreased  from  64.3  to  47.7  per  cent. 
The  pulp  obtained  when  using  2.1  pounds  of  sodium  sulphide  was 
slightly  undercooked  and  somewhat  brittle.  The  other  pulps  had 
fair  strength  and  wearing  properties  and  could  be  used  for  making 
a  medium  grade  of  wrapping  paper. 

As  the  amount  of  sodium  sulphide  was  increased,  the  disagreeable 
odor  arising  from  the  cooking  was  more  noticeable,  being  much  more 
offensive  for  cook  37  (50  pounds  Na2S  per  100  pounds  of  wood)  than 
for  cook  31  (7.5  pounds  Na2S).  Increasing  the  amount  of  sodium 
sulphide  resulted  in  lighter-colored  pulps,  that  from  cook  37  being 
considerably  lighter  in  color  than  from  cook  31. 

Sodium  sulphide  is  not  so  severe  in  its  action  on  wood  as  caustic 
soda.  A  cook  of  8  hours'  duration  was  made  with  sodium  sulphide 
only,  using  40  pounds  per  100  pounds  of  wood  and  a  maximum  cook- 
ing pressure  of  100  pounds  per  square  inch.  A  yield  of  41  per  cent 
was  obtained,  while  a  similar  cook  using  caustic  soda  alone  in  the 
proportion  of  20  pounds  per  100  pounds  of  wood  had  a  yield  of  44.3 
per  cent.  This  indicates  that  caustic  soda  is  almost  twice  as  effective 
as  sodium  sulphide  in  reducing  the  wood  to  pulp.  The  color  of  the 
pulp  produced  when  using  caustic  soda  alone  was  lighter  than  when 
using  sodium  sulphide  alone. 

EFFECTS  OF  SODIUM  CARBONATE. 

Sodium  carbonate  occurs  in  the  commercial  sulphate  liquors  due  to 
incomplete  causticization.  That  it  is  of  no  assistance  in  reducing 
longleaf  pine  was  show'n  by  a  cook  made  with  40  pounds  of  this 
chemical,  10  pounds  of  caustic  soda,  and  5  pounds  of  sodium  sulphide 
per  100  pounds  of  wood.  The  duration  of  cooking  was  7  hours  and 


18  BULLETIN   72,   IT.    S.    DEPARTMENT   OF   AGRICULTURE. 

the  maximum  gauge  pressure  was  100  pounds  per  square  inch.  The 
product  came  from  the  autoclave  in  the  form  of  hard,  black  chips 
which  were  quite  "raw"  on  the  inside;  the  yield  was  not  determined. 
In  comparison  with  this  result,  cook  40  (Table  6),  using,  per  100 
pounds  of  wood,  10  pounds  of  caustic  soda,  5  pounds  of  sodium  sul- 
phide, and  5  pounds  of  sodium  sulphate  (the  latter  being  of  no 
assistance  in  cooking),  also  afforded  a  product  in  the  chip  form. 
These  chips,  however,  were  soft,  and  could  easily  be  picked  apart  with 
the  fingers.  Of  the  3  hours'  total  duration  for  this  cook,  2.3  hours 
were  at  a  maximum  pressure  of  90  pounds.  The  yield  was  65.7  per 
cent.  While  it  is  hardly  safe  to  base  a  general  conclusion  upon  a  single 
trial,  this  test  indicates  that  sodium  carbonate,  at  least  when  present 
in  considerable  quantity,  retards  or  diminishes  the  effects  of  the 
caustic  soda  and  sodium  sulphide. 

EFFECTS  OF  SODIUM  SULPHATE. 

Sodium  sulphate  is  present  in  the  commercial  cooking  liquors,  due 
to  incomplete  reduction  of  the  sulphate  to  sulphide  during  the  smelt- 
ing operations.  Like  sodium  carbonate,  it  is  of  practically  no  assist- 
ance in  cooking.  A  cook  of  3  hours'  duration  and  90  pounds  maxi- 
mum gauge  pressure  was  made,  using  sodium  sulphate  in  the  propor- 
tion of  50  pounds  per  100  pounds  of  wood,  which  yielded  86.3  per  cent, 
while  another  cook  of  the  same  duration  and  pressure  but  without 
any  chemicals  whatever  (that  is,  using  pure  water  alone)  had  a  yield 
of  89.1  per  cent.  Allowing  for  experimental  errors,  there  was  little 
difference  between  the  results  of  these  two  cooks,  and  in  neither  case 
could  the  product  be  beaten  into  pulp. 

A  cook  was  also  made,  using  40  pounds  of  sodium  sulphate,  10 
pounds  of  caustic  soda,  5  pounds  of  sodium  carbonate,  and  5  pounds 
of  sodium  sulphide  per  100  pounds  of  wood;  the  duration  was  eight 
hours  and  the  maximum  gauge  pressure  was  100  pounds  per  square 
inch.  Only  hard  black  chips  were  obtained,  of  no  value  whatever 
for  pulp.  As  in  the  case  of  the  sodium  carbonate,  there  is  an  indica- 
tion that  sodium  sulphate  retards  the  action  of  the  other  chemicals. 
To  prove  this  further  tests  are  necessary. 

EFFECTS  OF  VARYING  ALL  CHEMICALS  IN  SAME  PROPORTION. 

A  series  of  tests  was  made  varying  the  amounts  of  all  sodium  com- 
pounds present  in  sulphate  cooking  liquors.  The  several  constituents 
were  kept  constant  in  regard  to  each  other  in  the  proportion  of  50 
parts  caustic  soda,  25  parts  sodium  sulphide,  and  25  parts  sodium 
sulphate.  For  convenience  the  amounts  of  the  different  chemicals 
have  been  computed  to  a  common  basis,  and  the  combined  values  are 
expressed  as  Na2O  (sodium  oxide). 


SUITABILITY   OF    LONGLEAF    PINE   FOR  PAPER   PULP. 


19 


The  yields  shown  in  Table  6  varied  from  65.7  per  cent  for  14.5 
pounds  of  total  Na2O  per  100  pounds  of  wood  to  36.8  per  cent  for 
72.5  pounds  of  total  Na2O.  The  conditions  indicated  for  cook  31 
afforded  the  best  results  with  regard  to  both  yield  and  quality  of 
pulp  produced.  With  the  higher  yields  the  pulps  were  harsh  and 
had  less  resistance  to  wear.  Nevertheless,  wrapping  papers  of 
medium  grades  could  be  made  from  these  pulps.  The  pulp  from 
cook  30  was  of  good  quality,  with  strength  and  wearing  properties 
equal  to  that  from  cook  31,  but  the  yield  was  not  so  high.  Cooks 
43,  26,  and  38  were  duplicates  of  each  other,  and  show  the  accuracy 
attained  in  the  yield  determinations.  The  pulps  from  these  three 
cooks  were  soft  and  fluffy,  and  had  poor  strength  and  wearing  prop- 
erties, due  to  overcooking. 

TABLE  6. — Effect  of  varying  amounts  of  all  sodium  compounds  on  the  yield  of  pulp. 

Weight  of  chips  charged  (bone-dry  basis) pounds. .    0. 996  to  1. 007 

Water  in  chips per  cent. .  10. 2     to  11. 5 

Causticity  of  liquor  charge do 53. 2     to  54. 3 

Sulphidity  of  liquor  charge do 27. 4     to  27. 9 

Initial  volume  of  digester  liquors  per  pound  of  chips  (bone-dry  basis) gallons. .    0. 675  to   0. 683 

Duration  of  cooking,  total hours. . 

Duration  of  cooking,  at  zero  gauge  pressure do 

Duration  of  cooking,  at  maximum  gauge  pressure do 

Maximum  gauge  pressiire  per  square  inch pounds. . 

Total  duration  of  oeater  treatment  (at  light  brush  only) hours. .       0,  1,  or  2 


3.0 
0.1 
2.0     to   2.3 


Cook 

No. 

Liquor  charge,  initial  concentrations. 

Chemicals  charged  per  100  pounds  of 
chips  (bone-dry  basis). 

Yield  of 
crude 
pulp 
(bone- 
dry 
basis). 

NaOH. 

Na^S. 

Na2S04. 

All  so- 
dium 
com- 
pounds 
as  NazO. 

NaOH. 

Na2S. 

Na2S04. 

All  so- 
dium 
pounds 
as  NasO. 

40 
39 
31 
30 
43 
26 
38 

Grams, 
per  liter. 
17.6 
21.2 
26.3 
35.6 
88.2 
88.8 
88.2 

Grams, 
per  liter. 
8.8 
10.6 
13.1 
17.8 
45.3 
44.4 
44.1 

Grams, 
per  liter. 
8.8 
10.6 
13.1 
17.8 
45.3 
44.4 
44.1 

Grams, 
per  liter. 
25.5 
30.7 
38.1 
51.3 
128.3 
126.8 
127.6 

Pounds. 
10.0 
12.0 
15.0 
20.0 
49.8 
50.0 
50.0 

Pounds. 
S.O 
6.0 
7.5 
10.0 
25.0 
25.0 
25.0 

Pounds. 
5.0 
6.0 
7.5 
10.0 
25.6 
25.0 
25.0 

Pounds. 
14.5 
17.4 
21.7 
28.9 
72.5 
171.4 
172.4 

Per  cent. 
65.7 
60.2 
52.0 
47.0 
36.8 
37.6 
36.6 

(P.  L.— 138,  S.  L.— 36.) 

1  The  NajO  values  for  cooks  26  and  38  differ  mainly  because  of  different  amounts  of  NajCOa  which  are  not 
separately  recorded  in  the  table. 

EFFECTS  OF  SODIUM  CHLORIDE. 

A  few  tests  were  made  to  determine  whether  or  not  the  use  of 
sodium  chloride  in  conjunction  with  caustic  soda  would  result  in  firmer 
and  less  fuzzy  pulps,  more  resistant  to  wear,  than  are  ordinarily  pro- 
duced with  the  soda  process.  If  this  were  possible  a  process  might  be 
developed  to  produce  pulps  similar  to  those  obtained  with  the  sulphate 
process  without  the  disagreeable  odors  so  characteristic  of  it.  Table  7 
shows  a  comparison  between  cooks  made  with  caustic  soda  alone  and 
with  caustic  soda  and  sodium  chloride.  It  is  not  probable  that  sodium 


20 


BULLETIN    72,    U.    S.    DEPARTMENT   OF   AGRICULTURE. 


chloride  has  an  effect  on  the  yield,  as  is  evidenced  by  the  data  for 
cooks  128  and  137.  Both  cooks  employed  20  pounds  of  caustic  soda 
per  100  pounds  of  wood,  but  the  former  used  5  pounds  of  sodium 
chloride  in  addition.  The  yields  from  the  two  cooks  were  identical. 
The  use  of  sodium  chloride  appeared  to  improve  the  qualities  of  the 
pulps  somewhat,  but  they  were  much  inferior  to  sulphate  pulps  at 
similar  yields.  The  few  advantages  attending  the  use  of  sodium 
chloride  preclude  the  possibility  of  this  modification  of  the  soda 
process  being  of  commercial  value. 

TABLE  7. — Effect  of  sodium  chloride  (NaCl)  used  in  conjunction  with  caustic  soda  (NaOH) 

on  the  yield  of  pulp. 

Weight  of  chips  charged  (bone-dry  basis) pounds. .    0. 910  to   1. 043 

Water  in  chips per  cent. .  15. 1     to  22. 0 

Causticity  of  liquor  charge  (disregarding  NaCl) do 96. 0     to  97. 2 

Duration  of  cooking  at  zero  gauge  pressure hours. .  0. 1 

Maximum  gauge  pressure  per  square  inch pounds. .  90 

Total  duration  of  beater  treatment  (at  light  brush  only) hours . .  2 


Cook 
No. 

Liquor  charge,  in- 
itial   concentra- 
tions. 

Chemicals  charged 
per  100  pounds 
of  chips  (bone- 
dry  basis). 

Initial  vol- 
ume of 
digester 
liquors  per 
pound  of 
chips 
(bone-dry 
basis). 

Duration  of  cook- 
ing. 

Yield  of 
crude 

(bone- 
dry 
basis). 

NaOH. 

NaCl.i 

NaOH. 

NaCU 

Total. 

At  maxi- 
mum 
gauge 
pressure. 

118 
122 
128 
137 

72 

Grams 
per  liter. 
44.2 
41.1 
49.2 
36.3 
35.2 

Grams 
per  liter. 
28.6 
20.0 
12.0 
0 
0 

Pounds. 
15.0 
20.0 
20.0 
20.0 
20.0 

Pounds. 
10.0 
10.0 
5.0 
0 
0 

Gallons. 
0.420 
.600 
.500 
.662 
.681 

Hours. 
3.0 
4.0 
6.0 
6.0 
3.0 

Hours. 
2.5 
3.5 
5.3 
5.3 
2.3 

Per  cent. 
73.9 
63.5 
58.9 
58.9 
71.6 

(P.  L.— 138,  S.  L— 176.) 
i  The  values  shown  represent  common  table  salt  and  not  the  pure  chemical. 

EFFECTS  OF  SULPHUR. 

Cooks  using  "flowers  of  sulphur"  and  caustic  soda  as  the  cooking 
chemicals  produced  pulps  almost  identical  with  those  resulting  from 
the  sulphate  process.  The  addition  of  sulphur  undoubtedly  im- 
parted to  the  pulps  the  resistance  to  wear  and  strength  not  obtainable 
by  the  soda  process  alone.  These  cooks,  however,  were  character- 
ized by  the  same  disagreeable  odor  as  the  sulphate  cooks,  and  this 
modification  of  the  soda  process  seems  to  have  no  particular  tech- 
nical advantage  over  the  sulphate  process  except  in  the  matter  of 
control  of  the  cooking  liquors. 

EFFECTS  OF  VARYING  THE  PRESSURES  OR  TEMPERATURES  OF  COOKING. 

In  the  sulphate  process,  as  in  the  soda  process,  the  digester  pres- 
sures represent  the  pressure  of  saturated  steam,  since  no  other 
gases  are  present  in  sufficient  quantity  to  affect  the  pressure.  This 


SUITABILITY   OF   LONGLEAF   PINE   FOR  PAPER   PULP. 


21 


was  determined  by  actual  test.  The  digester  pressures,  therefore, 
correspond  to  the  temperatures  of  saturated  steam;  and  values  of 
each  may  be  converted  into  the  other  by  means  of  standard  steam 
tables. 

Table  8  shows  the  effect  on  yield  of  variations  of  pressure  from  40 
to  140  pounds  per  square  inch.  As  the  pressures  increased,  the 
yields  decreased.  Cook  45,  with  a  pressure  of  40  pounds  per  square 
inch,  resulted  in  a  product  so  much  undercooked  that  no  pulp  could 
be  prepared  from  it.  The  yield,  of  course,  was  very  high.  Cook  46, 
using  a  pressure  of  140  pounds  per  square  inch,  resulted  in  50  per 
cent  yield.  For  intermediate  pressures  the  yields  were  correspond- 
ingly higher. 

TABLE  8. — Effect  of  varying  pressures  on  the  yield  of  pulp. 

Weight  of  chips  charged  (bone-dry  basis) pounds. . .  1. 000  to    1. 005 

Water  in  chips, per  cent. .  10. 4     to  11. 0 

Causticity  ofliquorcharge do 53.5 

Sulphidity  of  liquor  charge do 27. 4 

Initial  volume  of  digester  liquors  per  pound  of  chips  (bone-dry  basis) gallons. . .  0. 667  to   0. 680 

Duration  of  cooking,  total . .  hours. .  3. 0 

Duration  of  cooking  at  zero  gauge  pressure do 0. 1 

Duration  of  cooking  at  maximum  gauge  pressure do 2.0     to  2.3 

Total  duration  of  beater  treatment  (at  light  brush  only) do 0        or  1 


Liquor  charge,    initial   con- 
centrations. 

Chemicals   charged   per   100 
pounds  of  chips  (bone-dry 
basis) 

Yield  of 

Cook 
No. 

NaOH. 

Na«S.i 

All 
sodium 
com- 

NaOH. 

All 
sodium 
com- 

gauge 
pressure. 

pulp 
(bone-dry 
basis). 

pounds 

pounds 

asNaaO. 

as  Na2O. 

Grams 

Grams 

Grams 

per  liter. 

per  liter. 

per  liter. 

Pounds. 

Pounds. 

Pounds. 

Pounds. 

Per  cent. 

45 

21.3 

10.6 

30.8 

12.0 

6.0 

17.4 

40 

(2) 

42 

21.1 

10.6 

30.6 

12.0 

6.0 

17.4 

80 

61  3 

39 

21.2 

10.6 

30.7 

12.0 

6.0 

17.4 

.90 

60.2 

41 

21.1 

10.6 

30.6 

12.0 

6.0 

17.4 

120 

54.0 

46 

21.3 

10.6 

30.8 

12.0 

6.0 

17.4 

140 

50.0 

1  The  same  values  apply  to  the 


(P.  L.— 138,  S.  L.— 3  6.) 
2  Wood  not  cooked;  no  pulp  prepared. 


Pulps  produced  with  the  higher  pressures  were  stronger  and  had 
better  wearing  properties  than  those  resulting  from  the  lower  pres- 
sures. With  lower  pressures  the  pulps  became  more  and  more 
brittle  and  gradually  lost  their  soft,  pliable,  leather-like  feel.  The 
pulps  resulting  from  the  lower  pressures  were  the  more  brown  in 
color. 

The  best  pressure  conditions  for  these  tests  seemed  to  be  from  100 
to  140  pounds  per  square,  inch.  If  larger  amounts  of  chemicals  had 
been  employed,  pulps  of  the  same  yield  and  properties  would  prob- 
ably have  resulted  from  pressures  of  80  to  100  pounds  per  square 
inch. 


22 


BULLETIN   72,   U.   S.   DEPARTMENT  OF  AGRICULTURE. 


EFFECTS  OF  VARYING  THE  DURATIONS  OF  COOKING. 

Since  the  tirne  from  the  start  of  a  cook  until  maximum  pressure  was 
obtained  in  the  autoclave  was  practically  constant  (varying  from 
0.5  to  0.7  hour),  only  the  total  duration  of  cooking  will  be  considered. 
Table  9  shows  how  the  yields  were  affected  for  total  durations  varying 
from  one  to  nine  hours  in  three  series  of  tests,  using  high,  medium, 
and  low  amounts  of  chemicals.  In  the  case  of  the  first  series,  em- 
ploying very  high  amounts  of  chemicals,  55.9  per  cent  of  the  wood 
(giving  a  yield  of  44.1  per  cent)  was  dissolved  during  two  hours  of 
cooking,  while  by  cooking  for  seven  hours  longer  an  additional  loss 
of  only  12.8  per  cent  occurred.  Cook  124,  with  a  total  duration  of 
but  one  hour,  afforded  the  best  pulp  and  the  highest  yield  for  this 
series.  This  pulp  came  from  the  autoclave  in  the  form  of  soft  chips, 
and  the  resultant  paper  made  from  the  beaten  pulp  was  firm  and 
strong,  with  good  resistance  to  wear.  The  other  pulps  were  soft 
and  fuzzy,  due  to  overcooking.  As  the  duration  increased,  the 
color  of  the  pulps  changed  from  brown  (cook  124)  to  light  gray 
(cook  78). 

TABLE  9. — Effect  of  varying  durations  of  cooking  on  the  yield  of  pulp. 

Weight  of  chips  charged  (bone-dry  basis), pounds. .    0. 964  to  1. 034 

Water  in  chips per  cent. .  16. 0    to 24. 4 

Causticity  of  liquor  charge do 51.6    to  53. 3 

Sulphidity  of  liquor  charge do 26. 5     to  27. 4 

Initial  volume  of  digester  liquors  per  pound  of  chips  (bone-dry  basis) gallons . .  0. 667  to  0. 680 

Duration  of  cooking  at  zero  gauge  pressure hours. .  0. 1 

Maximum  gauge  pressure  per  square  inch pounds. .  90 

Total  duration  of  beater  treatment  (at  light  brush  only) hours..    1.5     or  2 

FIRST  SERIES. 


Liquor  charge,  initial  concen- 
trations. 

Chemicals  charged  per   100 
pounds  of  chips  (bone-dry 
basis). 

Duration  of  cooking. 

Yield  of 

Cook 

No. 

NaOH. 

Na2S.i 

All 
sodium 
com- 

NaOH. 

Na2S.i 

All 
sodium 
com- 

Total. 

At  maxi- 
mum 

pulp 
(bone-dry 

basis). 

pounds 
as  Na20. 

pounds 
as  Na20. 

gauge 
pressure. 

Grams 

Grams 

Grams 

per  liter. 

per  liter. 

per  liter. 

Pounds. 

Pounds. 

Pounds. 

Hours. 

Hours. 

Per  cent. 

124 

71.9 

36.0 

104.7 

40.0 

20.0 

58.3 

1.0 

0.5 

57.4 

125 

71.9 

36.0 

104.7 

40.0 

20.0 

58.3 

2.0 

1.5 

44.1 

80 

72.0 

36.0 

104.7 

40.0 

20.0 

58.2 

5.0 

4.3 

37.8 

78 

72.0 

36.0 

108.1 

40.0 

20.0 

60.1 

9.0 

8.3 

31.3 

SECOND  SERIES. 


123 

44.9 

22.5 

65.4 

25.0 

12.5 

36.4 

1.0 

0.5 

68.6 

126 

44.9 

22.5 

65.4 

25.0 

12.5 

36.4 

2.0 

1.5 

48.5 

84 

45.0 

22.7 

65.6 

25.0 

12.6 

36.5 

5.0 

4.3 

45.0 

83 

45.0 

22.7 

65.6 

25.0 

12.6 

36.5 

9.0 

8.3 

38.2 

THIRD  SERIES. 


86 

21.6 

10.8 

31.4 

12.0 

6.0 

17.4 

1.0 

0.3 

80.9 

127 

21.6 

10.8 

31.6 

12.0 

6.0 

17.6 

2.0 

1.5 

66-7 

88 

21.2 

10.6 

30.8 

12.0 

6.0 

17.4 

5.0 

4.3 

59.0 

87 

21.6 

10.8 

31.4 

12.0 

6.0 

17.4 

9.0 

8.3 

57.0 

i  The  same  values  apply  to  the  Na2SOrf  used. 


(P.  L.— 138,  S.  L.— 176.) 


SUITABILITY  OF   LONGLEAF   PINE   FOR  PAPEE  PULP.  23 

In  the  second  series,  when  medium  amounts  of  chemicals  were 
used,  prolonging  the  durations  of  cooking  likewise  resulted  in 
decreasing  the  yields.  The  yield  for  cook  123,  with  a  total  duration 
of  one  hour,  was  68.6  per  cent;  and  cook  83,  with  a  total  duration  of 
9  hours,  had  a  yield  of  38.2  per  cent.  With  a  2-hours'  duration  the 
amount  of  the  wood  dissolved  was  51.5  per  cent  (48.5  per  cent  yield), 
while  with  a  7-hours'  longer  cooking  period  the  loss  was  only  10.3  per 
cent  additional.  The  best  kraft  pulps  were  obtained  from  cooks  126 
and  84,  with  total  durations  of  2  and  5  hours,  respectively.  The 
resultant  papers  were  firm  and  strong,  and  resistant  to  wear.  Cook 
123,  using  a  duration  of  1  hour,  resulted  in  a  weak,  brittle,  and  under- 
cooked  pulp,  while  the  pulp  from  cook  83,  which  had  a  duration  of  9 
hours,  was  soft,  fluffy,  and  evidently  overcooked. 

The  same  general  effects  resulted  from  varying  the  durations  in  the 
third  series  of  tests  in  which  comparatively  low  amounts  of  chemicals 
were  employed.  In  this  case,  however,  the  best  pulps  were  produced 
with  the  longer  durations,  5  hours  for  cook  88  and  9  hours  for  cook  87. 
The  tests  employing  shorter  durations  resulted  in  weak  and 
brittle  pulps,  due  to  undercooking.  The  pulp  from  cook  88  was 
slightly  inferior  to  that  from  cook  87,  but  both  would  be  considered 
of  fair  quality  for  making  kraft  wrapping  paper. 

The  results  from  the  three  series  of  tests  indicate  that  cooks 
employing  high  amounts  of  chemicals  and  very  short  durations  will 
afford  pulps  of  a  quality  and  yield  similar  to  those  obtained  when 
using  medium  amounts  of  chemicals  and  medium  durations  and  to 
those  resulting  from  the  use  of  low  amounts  of  chemicals  and  com- 
paratively long  durations.  It  is  evident,  however,  that  much  more 
careful  control  of  the  operations  must  be  exercised  in  order  to  obtain 
consistent  results  when  high  amounts  of  chemicals  are  employed. 

EFFECTS  OF  VARYING  THE  INITIAL  CONCENTRATIONS. 

In  each  of  two  series  of  tests  varying  the  initial  concentrations  of 
chemicals  in  the  liquor  charge  the  amounts  of  chemicals  per  100 
pounds  of  wood  were  held  constant  as  follows:  15  pounds  of  caustic 
soda,  7.5  pounds  of  sodium  sulphide,  and  7.5  pounds  of  sodium 
sulphate  for  the  first  series,  and  12  pounds  of  caustic  soda,  6  pounds 
of  sodium  sulphide,  and  6  pounds  of  sodium  sulphate,  for  the  second 
series.  Since  the  amounts  of  chemicals  were  held  constant,  and  the 
concentrations  varied,  the  initial  volumes  of  digestor  liquors  per  pound 
of  chips  also  varied  accordingly.  Table  10  shows  the  effect  of  the 
varying  concentrations  en  the  yield  of  pulp. 


24 


BULLETIN   72,   U.   S.   DEPARTMENT   OF   AGRICULTURE. 


TABLE  10. — Effect  of  varying  initial  concentrations  on  the  yield  of  pulp. 
Weight  of  chips  charged  (bone-dry  basis) pounds. .    0. 964  to  1. 


Water  in  chips per  cent. .  16. 4 

Causticity  of  liquor  charge do 52. 8 

SUiphidity  of  liquor  charge do 27. 2 

Duration  of  cooking,  total hours. . 

Duration  of  cooking,  at  zero  gauge  pressure do 

Duration  of  cooking  at  maximum  gauge  pressure do 2. 0 

Maximum  gauge  pressure  per  square  inch pounds. . 

Total  duration  of  beater  treatment  (at  light  brush  only) hours. 

Chemicals  charged  per  100  pounds  of  chips  (bone-dry  basis): 

NaOH pounds. 

Na2S do... 

Na2S04 do... 

All  sodium  compounds  as  Na2O do. . . 


to  24. 4 
to  53. 6 
to  27. 5 
3.0 
0.1 

to  2.5 
90 
2 

First    Second 
series,     series. 
15. 0        12. 0 
7. 5          6. 0 
7.5          6.0 
21.8        17.5 


FIRST  SERIES. 


Cook 
No. 

Liquor  charge,  initial  concentrations. 

Initial  volume 
of  digester 
liquors  per 
pound  of  chips 
(bone-dry  basis). 

Yield  of 
crude  pulp 
(bone-dry 
basis). 

NaOH. 

NajS. 

Na2S04. 

All  sodium 
compounds 
as  Na2O. 

Grams 

Grams 

Grams 

Grams 

89 

per  liter. 
60.0 

per  liter. 
30.0 

per  liter. 
30.0 

per  liter. 

87.2 

Gallons. 
0.300 

Per  cent. 

47.9 

90 

45.0 

22.5 

22.5 

65.1 

.400 

53.3 

91 

36.0 

18.0 

18.0 

52.1 

.500 

55.2 

93 

30.0 

15.0 

15.0 

43.6 

.600 

58.6 

94 

25.7 

12.9 

12.9 

37.4 

.^00 

61.3 

95 

22.5 

11.2 

11.2 

32.7 

.800 

64.4 

96 

20.0 

10.0 

10.0 

29.0 

.900 

66.4 

97 

18.0 

9.0 

9.0 

26.1 

1.000 

66.9 

SECOND  SERIES. 


112 

72.0 

36.0 

36.0 

104.9 

0.200 

51.0 

100 

49.7 

24.8 

24.8 

72.0 

.290 

51.1 

101 

36.0 

18.0 

18.0 

52.2 

.400 

52.3 

105 

28.8 

14.6 

14.4 

42.2 

.500 

56.0 

114 

24.0 

12.0 

12.0 

35.0 

.600 

62.6 

106 

20.6 

10.3 

10.3 

30.0 

.700 

60.6 

107 

18.0 

9.0 

9.0 

26.2 

.800 

66.0 

108 

16.0 

8.0 

8.0 

23.3 

.900 

67.4 

115 

14.4 

7.2 

7.2 

21.0 

1.000 

67.3 

110 

12.0 

6.0 

6.0 

17.5 

1.200 

67.8 

111 

10.3 

5.1 

5.1 

15.0 

1.400 

67.4 

(P.  L.— 138,  S.  L.— 176.) 

When  the  concentration  of  all  sodium  chemicals  expressed  as 
Na2O  was  varied  from  26.1  to  87.2  grams  per  liter  (first  series  of 
tests)  the  resultant  yield  decreased  from  66.9  to  47.9  per  cent.  The 
best  results,  considering  both  yield  and  quality  of  pulps,  were  obtained 
from  cooks  91  and  93,  using  Na2O  concentrations  of  52.1  and  43.6 
grams  per  liter,  respectively.  Pulps  produced  from  cooks  having 
lower  concentrations  were  brittle  and  lacked  strength  and  wearing 
properties.  In  the  second  series  of  tests,  using  somewhat  smaller 
amounts  of  chemicals,  the  higher  concentrations  afforded  the  better 
results.  The  best  pulp  with  regard  to  strength  and  wearing  proper- 
ties was  that  obtained  from  cook  112,  using  a  Na2O  concentration  of 
104.9  grams  per  liter.  The  pulps  .obtained  when  using  a  concen- 
tration of  35  grams  per  liter  or  less  were  quite  brittle,  and  had  little 
strength  and  poor  wearing  properties. 


SUITABILITY   OF   LONGLEAF   PINE   FOE  PAPER   PULP.  25 

SUMMARY  OF  CONCLUSIONS  FROM  THE  AUTOCLAVE  TESTS. 

(1)  The  effective  cooking  chemicals  in  sulphate  cooking  liquors 
are  caustic  soda  and  sodium  sulphide,  the  former  being  the  more 
drastic  in  its  action.     Sodium  sulphate  and  sodium  carbonate,  which 
unavoidably  occur  in  the  commercial  liquors,  are  of  no  assistance  in 
cooking,  at  least  so  far  as  the  wood  of  longleaf  pine  is  concerned. 

(2)  Increases  in  the  amounts  of  either  caustic  soda  or  sodium 
sulphide,  or  both,  result  in  more  thorough  cooking.     The  same  effect 
may  be  obtained  by  increasing  either  the  cooking  pressure,  the  dura- 
tion of  cooking,  or  the  initial  concentrations  of  the  chemicals  in  the 
cooking  liquors. 

(3)  More  thorough  cooking  is  evidenced  by  decreased  yields  and 
by  lighter  colored  pulps  until  a  condition  of  very  thorough  cooking  is 
reached,  after  which  the  color  of  the  pulp  is  not  affected. 

(4)  The  best,  or  well-cooked,  sulphate  kraft  pulps  will  have  good 
strength  and  wearing  properties,  will  be  light  brown  in  color,  and 
will  have  a  smooth,  firm,  leather-like  feel  when  properly  beaten. 
Undercooked   pulps   are   characterized   by   a   darker   brown   color, 
brittleness,  lack  of  strength,  and  poor  wearing  properties.     Over- 
cooked pulps  are  light  gray  in  color  and  may  have  good  strength 
and  wearing  properties  when  properly  beaten,  but  the  yield  will  be 
low.     Pulps  much  overcooked,  in  addition  to  being  light  gray  in 
color,  will  be  soft  and  fluffy,  with  little  strength. 

(5)  With  each  different  combination  of  the  cooking  conditions 
there  is  a  definite  minimum  amount  of  sodium  sulphide  which  must 
be  used  in  conjunction  with  the  caustic  soda  present  to  impart  to 
the  product  the  high  strength  and  good  wearing  properties  char- 
acteristic of  properly  cooked  sulphate  kraft  pulps. 

(6)  The  use  of  sodium  chloride  in  conjunction  with  caustic  soda 
improves  the  quality  of  the  pulp  to  a  slight  extent  only.     The  similar 
use  of  sulphur  results  in  pulps  having  properties  practically  the  same 
as  those  of  sulphate  pulps. 

(7)  As  the  proportion  of  sodium  sulphide  in  the  digester  charge  is 
increased,  the  disagreeable  odor  produced  in  the  cooking  operations 
becomes  more  pronounced. 

PRACTICAL  SIGNIFICANCE  OF  THE  EXPERIMENTS. 

While  the  present  experiments  are  not  complete,  they  show  con- 
clusively (1)  that  longleaf  pine  is  well  adapted  for  the  manufacture 
of  natural-color  kraft  pulps  and  papers;  (2)  that  the  sulphate  process 
of  pulp  making  applied  to  this  wood  affords  products  of  better  quality 
and  of  higher  yields  than  the  soda  process;  (3)  that  kraft  papers  can 
be  made  from  longleaf  pine  equal  or  superior  in  quality  to  the 
imported  and  domestic  kraft  papers  now  on  the  market;  and  (4) 


26  BULLETIN   72,   U.    S.   DEPARTMENT   OF  AGRICULTURE. 

that  the  high  gravity  of  the  wood  and  the  resultant  high  yield  of 
pulp  per  cord  give  longleaf  pine  an  advantage  possessed  by  few,  if 
any,  other  commercially  important  woods  suitable  for  pulp  making. 

The  autoclave  tests  indicate  that  there  should  be  a  certain  com- 
bination of  values  for  the  variable  cooking  conditions  which  will 
result  in  the  most  economical  method  of  operation.  However, 
other  factors  than  the  variables  thus  far  investigated  must  be  taken 
into  consideration  in  determining  what  this  combination  is.  For 
example,  the  proper  degree  to  which  a  pulp  must  be  cooked  will 
depend  partly  upon  the  cost  of  the  beater  treatment.  With  cheap 
power  for  beating,  the  pulp  need  not  be  so  severely  cooked  as  when 
the  cost  of  power  is  high.  The  best  concentrations  and  proportions 
of  chemicals  in  the  digester  liquors  will  likewise  depend  upon  the 
efficiency  of  the  recovery  system  and  the  method  of  operating  it. 

o 


WASHINGTON  :  GOVERNMENT  PRINTING  OFFICE  :    1914 


Gaylord  Bros. 

Makers 

Syracuse,  N.  Y. 
PAT.  JAM.  21 ,1908 


477615 

T 


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